﻿/*
Copyright (c) 2007-2011 William POTTIER - AllProgrammic

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights 
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies 
of the Software, and to permit persons to whom the Software is furnished to do so, 
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all 
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR 
IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
using System;
using System.Reflection;
using NetAccess.Common.Exceptions;

namespace NetAccess
{
    internal static class Singleton<T>
       where T : class
    {
        // ReSharper disable StaticFieldInGenericType
        static volatile T _instance;
        static readonly object Lock = new object();
        // ReSharper enable StaticFieldInGenericType


        // ReSharper disable EmptyConstructor
        static Singleton()
        {
        }
        // ReSharper restore EmptyConstructor

        internal static T Instance
        {
            get
            {
                if (_instance == null)
                    lock (Lock)
                    {
                        if (_instance == null)
                        {
                            ConstructorInfo constructor;

                            try
                            {
                                // Binding flags exclude public constructors.
                                constructor = typeof(T).GetConstructor(BindingFlags.Instance |
                                              BindingFlags.NonPublic, null, new Type[0], null);
                            }
                            catch (Exception exception)
                            {
                                throw new NetAccessException(exception);
                            }

                            if (constructor == null || constructor.IsAssembly)
                                // Also exclude internal constructors.
                                throw new NetAccessException(string.Format("A private or " +
                                      "protected constructor is missing for '{0}'.", typeof(T).Name));

                            _instance = (T)constructor.Invoke(null);
                        }
                    }

                return _instance;
            }
        }
    }
}
